1. Field of the Invention
The present invention relates to nucleotide fragments derived from the env gene of the caprine arthritis-encephalitis virus (CAEV) and to the corresponding peptide fragments and to their applications in the screening for caprine viral encephalitis and arthritis; the present invention also relates to anti-peptide fragment antibodies as well as to their applications in the diagnosis of viral encephalitis and arthritis.
2. Description of the Related Art
The caprine arthritis-encephalitis virus is a lentivirus which causes a leukoencephalitis in young goats and a chronic clinical arthritis in 20 to 30% of adult goats infected naturally. Arthritis is usually progressive and is particularly severe at the level of the synovial spaces of the carpal joints.
The nucleotide sequence of the CAEV-CO strain has been sequenced and described (M. SALTARELLI et al., Virol., 1990, 179, 347-364), using infectious clones obtained from HindIII fragments, transfected into goat synovial membrane cells. The genome comprises 9189 nucleotides and includes successively the sequence encoding LTR, the sequences encoding the different viral proteins: Gag protein, Pol protein, the regulatory protein Q, the Tat protein, the envelope proteins and the Rev proteins.
The organization of the env gene encoding the CAEV envelope glycoprotein is similar to that of the sheep viruses (VISNA virus) and comprises a sequence encoding a surface (SU) protein and a sequence encoding a transmembrane (TM) protein which form the envelope glycoprotein.
The CAEV envelope proteins are considered to be at the centre of the host-virus relationship; their study is therefore essential for understanding the interaction of the virus with the immune system (neutralizing epitopes, B and T epitopes) and with the target cells in the infection and for developing effective diagnostic reagents.
The seriousness of the disease in the infected animals is directly correlated with the level of anti-viral envelope (Env) protein antibody, and in particular with the level of anti-transmembrane (TM) protein antibody and/or with the level of anti-surface (SU) protein antibody of the said Env envelope protein (T. C. McGUIRE et al. J. Virol., 1992, H, 5, 3247-3250; D. P. KNOWLES et al., 1991, J. Virol., 1991, 65, 11, 5744-5750).
Indeed, the immune response to the viral antigen plays an important role in the inflammation of the joints (in particular, the inflammation of the synovial spaces of the carpal joints), especially because of a massive infiltration of the said joints by lymphocytes, plasmocytes and macrophages and by an accumulation of antibodies directed against the Env protein.
In particular, the serum having a high titer with respect to monomeric (38 kDa) and oligomeric TM glycoproteins are found in goats with progressive arthritis (D. P. KNOWLES et al., J. Virol., 1990, 64, 2396-2398).
Moreover, goats vaccinated with the inactivated caprine arthritis-encephalitis virus develop a more severe arthritis, after infection in the laboratory than the control animals (McGUIRE et al., J. Vet. Res., 1986, 47, 537-540).
It is therefore vital to establish a constant supervision of the herds in order to avoid propagation of the disease, in particular by excluding the diseased animals as rapidly as possible.
At present, CAEV arthritis is essentially diagnosed by means of serological tests based on a whole virus preparation; such tests have the disadvantage of being difficult to prepare and of being expensive; they also require a particularly delicate development (problem of standardization) and can, in addition, cause false-negative reactions and/or false-positive reactions.
Other tests (ELISA tests) also exist which use recombinant Gag proteins; such tests also have the disadvantage of causing false-negative and/or false-positive reactions and create, in addition, problems of background noise.
Now, in overview, it is absolutely vital to have a reliable and inexpensive test so as to be able to test the herds as a whole in order to avoid a massive infection (especially by milk) (programme of eradication).